1. Field of the Invention
This invention generally relates to a plasma display, and more particularly to a plasma display that is adaptive for improving brightness as well as discharge efficiency.
2. Description of the Related Art
Recently, a plasma display feasible to a manufacturing of a large-dimension panel has been highlighted as a flat panel display device. The plasma display usually controls a discharge period of each pixel in accordance with a digital video data to thereby display a picture. The plasma display typically includes a three-electrode, alternating current (AC) type plasma display that has three electrodes and is driven with an AC voltage.
FIG. 1 shows the manner in which each discharge cell is arranged in a related-art matrix-type, AC-type plasma display. This discharge cell includes an upper plate provided with a sustain electrode pair 14 and 16, an upper dielectric layer 18 and a protective film 20 that are sequentially formed on an upper substrate 10, and a lower plate provided with a data electrode 22, a lower dielectric layer 24, barrier ribs 26 and a phosphorous material layer 28 that are sequentially formed on a lower substrate 18. The upper substrate 10 and the lower substrate 18 are spaced in parallel by the barrier ribs 24.
Each electrode of the sustain electrode pair 14 and 16 is comprised of transparent electrodes 14A and 16A having a relatively large width and made from a transparent electrode material (e.g., ITO) to transmit a visible light, and metal electrodes 14B and 16B having a relatively small width to compensate for a resistance component of the transparent electrodes 14A and 16A. Such a sustain electrode pair 14 and 16 consists of a scan electrode and a sustain electrode. The scan electrode 14 is mainly supplied with a scan signal for panel scanning and a sustain signal for discharge sustaining. The sustain electrode 16 is mainly supplied with a sustain signal. Electric charges are accumulated in the upper and lower dielectric layers 18 and 24. The protective film 20 prevents a damage of the upper dielectric layer 18 caused by sputtering to thereby prolong the lifetime of the plasma display as well as to improve the emission efficiency of secondary electrons. This protective film 20 is usually made from MgO.
The address electrode 22 crosses the sustain electrode pair 14 and 16. This address electrode is supplied with a data signal for selecting discharge cells to be displayed. The barrier ribs are formed in parallel to the address electrode to thereby prevent an ultraviolet ray generated by the discharge from being leaked into adjacent discharge cells. The phosphorous material layer 28 is coated on the surfaces of the lower dielectric layer 24 and the barrier ribs to generate any one of red, green and blue visible lights. A discharge space is filled with an inactive gas for a gas discharge.
The discharge cell of the related-art plasma display having the aforementioned structure selects a discharge cell by an opposite discharge between the address electrode 22 and the scan electrode 14, and thereafter sustains discharge by a surface discharge between the sustain electrode pair 14 and 16. In the discharge cell, the phosphorous material layer is radiated by an ultraviolet ray generated upon sustain discharge to thereby emit a visible light from the cell. In this case, the plasma display controls a discharge sustain period, that is, a sustain discharge frequency of the discharge cell, in accordance with video data to thereby implement a gray scale required for an image display.
Such an AC surface-discharge plasma display makes a time-divisional driving of one frame, which is divided into a plurality of sub-fields, so as to realize gray levels of a picture. A light-emission having a frequency proportional to a weighting value of video data is made in each sub-field period to thereby express a gray level. For instance, if it is intended to display a picture of 256 gray levels using an 8-bit video data, one frame display interval (i.e., 1/60 second=about 16.7 msec) at each discharge cell 11 is divided into 8 sub-fields SF1 to SF8. Each of the 8 sub-fields SF1 to SF8 again is divided into a reset period, an address period and a sustain period, and the sustain period is given by a weighting value at a ratio of 1:2:4:8, . . . ,:128. Herein, the reset period is a period for initializing the discharge cell, the address period is a period for generating a selective address discharge in accordance with a logical value of video data, and the sustain period is a period for sustaining discharge at the discharge cell where the address discharge is generated. The reset period and address period are identically assigned in each sub-field interval.
If electrode widths of the scan electrode 14 and the sustain electrode 16 are formed narrowly in order to reduce power consumption of the plasma display, then a discharge path upon discharge is shortened to thereby limit an light-emission area. Thus, the amount of ultraviolet ray emission is reduced and hence brightness is deteriorated. Further, discharge at the discharge cell is generated in a manner diffused into a gap between the respective transparent electrodes 14A and 16A of the sustain electrode pair 14 and 16; that is, in a manner diffused from the center of the discharge cell into the ends of the transparent electrodes 14A and 16A. Accordingly, if it goes far away from the gap between the transparent electrodes 14A and 16A, then discharge efficiency is reduced and brightness also is reduced.
FIG. 2 shows a plasma display having a different electrode structure that includes projecting electrodes. In this plasma display, a sustain electrode pair 44 and 46 consists of stripe-type metal electrodes 44A and 46A formed in a stripe type and projecting electrodes 44B and 46B formed within the discharge cell and connected to the respective metal electrodes 44A and 46A.
The metal electrodes 44A and 46A are positioned at each edge of the discharge cell and are made from a metal material having good conductivity such as sliver (Ag) or copper (Cu). The projecting electrodes 44B and 46B have a relatively larger width than the metal electrodes 44A and 46B and are formed in opposing relation thereto.
In order to reduce the amount of current wasted from such a protrusion-type sustain electrode pair 44 and 46, the projecting electrodes 44B and 46B are formed to have a width (W) of about 200 μm to 250 μm and a length (L) of about 400 μm to 1000 μm. However, even though sizes of the projecting electrodes 44B and 46B have been set appropriately, an area occupied by the electrodes is reduced and hence a discharge voltage is increased, thereby causing a deterioration of discharge efficiency.
In order to overcome problems caused by the protrusion-type projecting electrode, a plasma display including T-type projecting electrodes has been proposed as shown in FIG. 3. In this plasma display, a sustain electrode pair 54 and 56 formed on an upper substrate (not shown) are comprised of stripe-type metal electrodes 54A and 56A and T-type projecting electrodes 54B and 56B which protrude from the metal electrodes 54A and 56A, respectively.
The T-type projecting electrodes 54B and 56B extend from the metal electrodes 54A and 56A and are opposed to each other in a T shape. The first electrode width W1 of the T-type projecting electrodes 54B and 56B is formed to be smaller than the second electrode width W2 thereof. Since the electrode width W2 at an opposite portion of the two T-type projecting electrodes 54B and 56B is large, it is not difficult to cause a discharge. Thus, even though the first electrode width W1 is small, brightness is not reduced largely and an area occupied by the electrodes is reduced to thereby decrease a wasted current amount.
However, in the plasma display including T-type projecting electrodes modifying the protrusion type, a distance W3 between the projecting electrodes 54B and 56B at each side and the barrier ribs 58 is not equal when a mis-alignment occurs upon joint of the substrates. An amount of absorbed electric charges is increased more, as it is closer to the barrier ribs 58. Thus, if a distance W3 between each side surface of the projecting electrodes 54B and 56B becomes different, then an amount of wall charges produced at each side upon discharge is differentiated.
FIG. 4 shows a plasma display which includes a transparent blank-type electrode, which is another electrode structure which has been proposed for plasma displays. This plasma display is comprised of transparent electrodes 34A and 36A having holes formed on an upper substrate, and metal electrodes 34B and 36B for compensating for resistance components of the transparent electrodes 34A and 36A.
The transparent electrodes 34A and 36A have a relatively large width and are made from a transparent electrode material such as ITO for the purpose of transmitting visible light. A hole 35 may be formed in a square shape or various polygonal shapes. Since holes 35 are formed at transparent electrodes 34A and 36A, an area of the transparent electrodes 34A and 36A are reduced. Accordingly, a capacitance value is reduced and hence power consumption is reduced. Also, an electrode area of the sustain electrode pair 34 and 36 is reduced, thereby increasing an aperture ratio.
However, the blank-type plasma display including sustain electrode pair 34 and 36 defines holes 35 at the transparent electrodes 34A and 36A to thereby somewhat improve power consumption, but it also raises a discharge-separation phenomenon in which two discharge modes are formed within a driving voltage. More specifically, as shown in FIG. 5, the transparent electrode 36A of the sustain electrode can be divided into A, B and C areas around the hole 35. If a discharge voltage is applied to the transparent electrode 36A, then a discharge is generated at the A area of the transparent electrode 36A positioned at the closest distance and then is diffused into the B and C areas. At this time, if a voltage is dropped within a sustain voltage margin, then an amount of accumulated wall charges becomes small because the B area has a small discharge area, and electric charges absorbs from the barrier rib 38 to thereby increase an amount of lost electric charge because it is positioned at a close distance from the barrier rib 38. Accordingly, the B area makes a small contribution to a plasma discharge, and a short pass discharge is limited to the A area to thereby separate the discharge into the A area and the C area and hence largely reduce brightness.
In the plasma display discharge cell structures described above, as shown in FIG. 6, a strong discharge is generated at the center of the discharge cell while weaker discharge is generated as the distance away from the center increases. Furthermore, a discharge is not generated at the edge area of the discharge cell. Accordingly, the related-art plasma display has problems in that discharge efficiency and brightness are deteriorated.
Also, the related-art plasma display discharge cell structures have a problem in that, because a distance between the metal electrodes is far away from the opposite surface of the transparent electrodes, power consumption caused by a resistance is large. The related-art plasma display discharge cell structures have another problem in that, because a distance between the metal electrodes from the opposite surface of the transparent electrodes is constant to thereby cause an initial discharge at all positions of the opposite surface, efficiency of the initial discharge is deteriorated.